02GF74
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| posted on 5/6/07 at 03:45 PM |
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offset bores
another hypothetical questions.
let's say someone wanted to increase the capacity of a engein e.g. rv8 or xflow and the limiting factor is the amount of metal between adjacent
bores.
reboring the cylinders so they are off line would get round that but when the pistons are at TDC, the conrod will not be vertical - will that matter?
(I don't know how many degrees it would be) but also the timing would need to change. Has this ever been done to an engine?
Instead of offseting the bores as above, how about overboring cylinder 1 and 4 and leaving the middle two original size. The increase will be bigger
than boring out all 4 by the same amount. With twin dcoe carbs, the fuelling can be adjusted so is there going to be a problem in having a 4 cylinder
engine with cylinders that are not of the same capacity? (firing order remains the same so you get big-normal-big-normal power strokes).
Again has this ever been tried in an engine, if not, why not?
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sebastiaan
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| posted on 5/6/07 at 04:01 PM |
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If the ignition timing is going to change (which it will...), the camshaft timing will need to change too. This means bespoke camshafts and thus mucho
money. It could hypothetically be done, though.
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NigeEss
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| posted on 5/6/07 at 04:08 PM |
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Consult David Vizards "Tuning the A Series Engine" for info about offset boring. Just
tried to find mine and appear to have lost/lent it 
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Mark Allanson
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| posted on 5/6/07 at 04:13 PM |
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The bores are always offset, something complicated that we we taught in college, it made sense at the time but I can't remember it now!
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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snapper
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| posted on 5/6/07 at 04:20 PM |
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Just posted a huge reply and lost it all so basicaly.
If you have 10mm between bores and need a minimum 5mm then yes you coud decided to only do 2 out of for but the rotational stresses would shake the
engine to bits.
Thats why we try and balance the engine so all the pistons and rods together weigh the same.
you may be able to get your new pistons and rods to weigh the same as the originals and as an engineering problem it is intreging, but i would think
not a real world solution
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Mal
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| posted on 5/6/07 at 04:27 PM |
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Offset bores
The VW VR6 engine is has a very shallow V of about 15 degrees. I recently saw some pictures of one with the head removed and it looks like a straight
6 with the bores off-set. There is one cylinder head which accomodates all 6 cylinders.
Mal
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Fatgadget
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| posted on 5/6/07 at 04:29 PM |
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quote:
Originally posted by 02GF74
another hypothetical questions.
let's say someone wanted to increase the capacity of a engein e.g. rv8 or xflow and the limiting factor is the amount of metal between adjacent
bores.
reboring the cylinders so they are off line would get round that but when the pistons are at TDC, the conrod will not be vertical - will that matter?
(I don't know how many degrees it would be) but also the timing would need to change. Has this ever been done to an engine?
Instead of offseting the bores as above, how about overboring cylinder 1 and 4 and leaving the middle two original size. The increase will be bigger
than boring out all 4 by the same amount. With twin dcoe carbs, the fuelling can be adjusted so is there going to be a problem in having a 4 cylinder
engine with cylinders that are not of the same capacity? (firing order remains the same so you get big-normal-big-normal power strokes).
Again has this ever been tried in an engine, if not, why not?
Offset boring is common on the A series lumps.I believe that is how capacities up to 1500cc are achieved.
Talking of overboring certain cylinders,apparently this was a dodge used by some racers. They would bore out cylinders 2,3,4,5,6,7 and 8 to the max.
Come scrutineering, only cylinder 1 was usually checked for compliance!
[Edited on 5/6/07 by Fatgadget]
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Fatgadget
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| posted on 5/6/07 at 04:31 PM |
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quote:
Originally posted by Mal
The VW VR6 engine is has a very shallow V of about 15 degrees. I recently saw some pictures of one with the head removed and it looks like a straight
6 with the bores off-set. There is one cylinder head which accomodates all 6 cylinders.
Mal
Ditto the Lancia Fulvia "V"4 of yesteryear.
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Ivan
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| posted on 5/6/07 at 05:08 PM |
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The best and quite possibly cheapest and most trouble free solution to more capacity is a bigger engine or a supercharger or turbo.
But it is a good question.
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goodall
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| posted on 5/6/07 at 05:08 PM |
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yep the vr series of engine has offset bores, they market it as 'V' engine but since each cylinder has its own journal its closer to being
a 'I' engine
these are found in the R32 (and probabily others in the range) as a offset 6 and in the passet in north america as a 5 cylinder i think and also in
the veyron as a W16 but its more like a a pair of vr8's (if there was such a thing) made into a 'V' engine it is marketed as a W16
but its really just a V16 with offset bores
[Edited on 5/6/07 by goodall]
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ned
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| posted on 5/6/07 at 08:17 PM |
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the top of the range passat is a w8. the v5 and v6 are offset bored and the vw/audi bently engine and all 'w' engines are v's with
2x offset banks of cylinders.
more reading and piccy's:
http://www.autozine.org/technical_school/engine/tech_engine_packaging.htm
beware, I've got yellow skin
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